009
FXUS65 KBYZ 220037
AFDBYZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BILLINGS MT
637 PM MDT SUN JUN 21 2026
KEY MESSAGES
- SCATTERED SHOWERS AND THUNDERSTORMS (30-70%) THROUGH THIS
EVENING. LOCALLY HEAVY RAIN IS POSSIBLE WITH THIS ACTIVITY,
ESPECIALLY EAST OF A HYSHAM TO SHERIDAN LINE.
- A COLD FRONT WILL FOCUS SHOWER AND THUNDERSTORM POTENTIAL
MONDAY. A FEW STRONG TO SEVERE STORMS ARE POSSIBLE MAINLY EAST
OF BILLINGS.
- MAINLY DRY AND TRENDING WARMER TUESDAY AND WEDNESDAY.
- WIDESPREAD SHOWER AND THUNDERSTORM CHANCES (30-50%) FORECAST
THURSDAY WITH A FEW STRONG STORMS POSSIBLE.
- HOT FRIDAY WITH HIGHS AROUND 90 DEGREES.
- A STRONG STORM SYSTEM MAY IMPACT THE REGION FROM FRIDAY NIGHT
THROUGH NEXT WEEKEND. WIDESPREAD PRECIPITATION AND MOUNTAIN
SNOW? STAY TUNED TO THE FORECAST THIS WEEK.
DISCUSSION
THIS AFTERNOON THROUGH SUNDAY...
SYNOPTIC OVERVIEW...WEAK FLOW ALOFT OVER THE AREA THIS AFTERNOON
WITH A MOIST ATMOSPHERE (PWATS NEAR 1.25 INCHES) RESIDING OVER
THE EASTERN HALF OF THE FORECAST AREA. A MODEST DISTURBANCE WILL
SLOWLY SHIFT EAST ALONG THE MT/CANADA BORDER TONIGHT INTO
TOMORROW. NORTHWEST WINDS WORKING AROUND THE BACK SIDE OF THIS
SYSTEM WILL PUSH A WEAK COLD FRONT THROUGH THE AREA (NW TO SE)
DURING THE DAY MONDAY. THIS WILL BE THE FOCUS FOR SCATTERED
SHOWERS AND THUNDERSTORMS MONDAY/MONDAY EVENING. NORTHWEST FLOW
ALOFT WILL PERSIST ON TUESDAY OVER THE AREA, BRINGING DRIER
CONDITIONS TO THE REGION, BUT NOT COMPLETELY ENDING PRECIPITATION
CHANCES.
AND THAT THEME OF NOT COMPLETELY ENDING PRECIPITATION CHANCES
WILL CONTINUE THROUGH THE WORK WEEK AS WE NEVER REALLY END THE
NORTHWEST FLOW ALOFT WHILE AT THE SURFACE A THERMAL LOW DEVELOPS
WEST OF THE DIVIDE WHICH WILL HELP PULL SOME FORM OF LOW LEVEL
EASTERLY FLOW, COULD BE NORTHEAST TO SOUTHEAST AT TIMES, OVER THE
AREA EACH DAY. THIS WILL HELP HOLD ENOUGH MOISTURE OVER THE AREA
FOR AFTERNOON/EVENING SHOWER AND THUNDERSTORM CHANCES IN PLACES
EACH DAY, WITH A WEAK DISTURBANCE THURSDAY PROVIDING THE BEST
CHANCES (30-40%.
A LARGE UPPER LEVEL STORM SYSTEM DROPS OUT OF THE GULF OF ALASKA
INTO THE THE PACIFIC NW COAST EARLY FRIDAY. AHEAD OF THIS STORM
SYSTEM SOUTHWEST FLOW WILL OVERSPREAD THE REGION PULLING HOTTER
AIR IN FROM THE GREAT BASIN. TEMPERATURES ARE FORECAST INTO THE
LOWER 90S FRIDAY, BUT LOW LEVEL WINDS REMAIN OUT OF THE
EAST/SOUTHEAST ACROSS THE AREA. THE LOW LEVEL MOISTURE ADVECTION
WILL KEEP FULL DOWNSLOPE EFFECTS FROM DEVELOPING THAT COULD PUSH
TEMPERATURES HIGHER. A STRONG CAPPING INVERSION IS LIKELY TO BE IN
PLACE GIVEN THIS DRY/WARM OVER-RUNNING SETUP SO THE FORECAST IS
DRY THROUGH THE AFTERNOON, BUT MID LEVEL COOLING ARRIVES BY THE
EVENING TO HELP BREAK THE CAP AND INCREASE PRECIPITATION CHANCES
(INCLUDING POTENTIALLY STRONG THUNDERSTORM CHANCES) THROUGH FRIDAY
NIGHT. THIS STORM SYSTEM SLIDES INTO THE NORTHERN ROCKIES AND SOME
MODEL SOLUTIONS KEEP IT OVER THE AREA INTO THE EARLY PORTION OF
NEXT WEEK. THIS SYSTEM HAS THE POTENTIAL FOR SIGNIFICANT
PRECIPITATION PRODUCTION, AND IS COLD ENOUGH FOR ACCUMULATING
MOUNTAIN SNOW WHERE THE CORE OF THE LOW TRACKS. STILL TOO EARLY
FOR SPECIFICS, BUT THOSE WITH OUTDOOR PLANS NEXT WEEKEND SHOULD
PAY CLOSE ATTENTION TO THE FORECAST THIS WEEK.
CONVECTION THIS AFTERNOON/EVENING...WITH THE RECENT RAINFALL AND
COOLER AIR ALOFT OVER THE AREA TODAY THERE IS PLENTY OF CAPE
AVAILABLE TO SUPPORT AFTERNOON AND EVENING CONVECTION. THE
LIMITING FACTOR WILL BE SHEAR AND A TRIGGER TO LIFT THE ATMOSPHERE
ENOUGH TO KICK START THUNDERSTORMS. MESO-ANALYSIS AT NOON SHOWS A
TONGUE OF ML- CAPE OF 500-1000J/KG OVER SHERIDAN, POWDER RIVER,
AND THE SOUTHERN HALF OF ROSEBUD COUNTY. THIS AREA IS ON THE
WESTERN EDGE OF THE EXTENSIVE CLOUD COVER AND SHOWER ACTIVITY FROM
THIS MORNING WHERE THE SUN IS WORKING ON THE PREVIOUSLY MENTIONED
MOIST ATMOSPHERE (PWATS NEAR 1.25 INCHES). DIFFERENTIAL HEATING
AND RESIDUAL OUTFLOW BOUNDARIES FROM OVERNIGHT CONVECTION LOOK TO
BE THE MAIN FORCING MECHANISM AND WOULD EXPECT ANY STORMS THIS
AFTERNOON AND EVENING TO STRUGGLE TO SUSTAIN THEIR UPDRAFTS GIVEN
THE LACK OF SHEAR (<20KTS). FURTHER WEST PWATS DROP TO HALF AN
INCH TOWARD THE WESTERN FOOTHILLS WITH LIGHT NORTHWEST WINDS
ADVECTING DRIER AIR INTO THE AREA, THUS EXPECT MORE ISOLATED
COVERAGE OF SHOWER AND THUNDERSTORMS. THE LATEST SATELLITE IMAGERY
SHOWS DEVELOPING CONVECTION DOWNSTREAM OF AREA MOUNTAIN RANGES
WHERE WEAK NEAR SURFACE CONVERGENCE IS ONGOING. LOCALLY HEAVY RAIN
WILL BE THE MAIN THREAT WITH STORMS DEVELOPING IN THE JUICIER
AIRMASS ALONG AND EAST OF A HYSHAM TO SHERIDAN LINE.
CONVECTION OVERNIGHT TONIGHT THROUGH MONDAY EVENING...ISOLATED TO
SCATTERED SHOWERS ARE FORECAST OVER THE WESTERN HALF OF THE AREA
OVERNIGHT TONIGHT AS THE UPPER TROF TO THE NORTH APPROACHES THE
AREA AND LOW LEVEL EASTERLY WINDS STRENGTHEN IN RESPONSE CREATING
CONVERGENCE AND WEAK UPSLOPE INTO THE FOOTHILLS. PRECIPITATION IS
EXPECTED TO BE LIGHT WITH THIS ACTIVITY AND A WEAK THUNDERSTORM OR
TWO CAN'T BE RULED OUT. THE WEAK COLD FRONT THAT WILL MOVE
THROUGH THE AREA DURING THE DAY TOMORROW WILL BE SUPPORTED BY AN
80-90KT JET STREAK. THIS WILL PROVIDE THE SHEAR TO SUPPORT
STRONGER THUNDERSTORM DEVELOPMENT BY EARLY AFTERNOON TOMORROW WITH
SPC DAY 2 OUTLOOK SHOWING A MARGINAL SEVERE THREAT ESSENTIALLY IN
THE SAME AREA AS THE HIGHER MOISTURE VALUES TODAY, EAST OF A
HYSHAM TO SHERIDAN LINE. THE SLIGHT RISK COME RIGHT UP TO THE
SOUTHERN BORDER IN CAMPBELL AND CROOK COUNTIES IN WYOMING. A
WRINKLE IN THIS SEVERE POTENTIAL WILL BE THE AMOUNT OF CLOUD COVER
AND ONGOING SHOWERS FROM THE MORNING HOURS WHICH MAY LIMIT
HEATING THUS INHIBIT STORM INITIATION AND STRENGTH, THE WAY IT DID
ON SATURDAY. THE LATEST HREF HAS ALSO SHIFTED THE STRONGER LONG
LIVED HELICITY TRACKS FROM IN THE MARGINAL RISK AREA FURTHER WEST
WITH THE STRONGEST BEGINNING OVER COLUMBUS AND TRACKING NEAR
BILLINGS THEN SOUTHEAST INTO SHERIDAN COUNTY. THIS FITS WITH WHERE
CLOUD COVER AND EARLY MORNING SHOWERS CLEAR OUT EARLIER ALLOWING
BETTER SUN AND HEATING FROM MID MORNING INTO THE EARLY AFTERNOON
HOURS. IF THIS TREND CONTINUES WOULD NOT BE SURPRISED TO SEE THE
MARGINAL RISK AREA EXPANDED FURTHER WEST TOWARD STILLWATER COUNTY.
ML/AI GUIDANCE SUGGESTS THE SLIGHT RISK MAY NEED TO COME A BIT
FURTHER NORTH INTO SHERIDAN, S. ROSEBUD, POWDER RIVER AND CARTER
COUNTIES WITH NCAR NEURAL NET SHOWING A 20% PROBABILITY FOR SEVERE
NUDGING INTO THESE AREAS. HAIL LOOKS LIKE THE MAIN THREAT BUT
STRONG WINDS AND LOCALLY HEAVY RAINFALL WILL ALSO BE IN THE MIX.
CONVECTION THURSDAY THROUGH NEXT WEEKEND...THE INGREDIENTS ARE
THERE FOR STRONGER THUNDERSTORMS TOWARD THE END OF THE WEEK. THE
NCAR ML/AI GUIDANCE SHOWING SOME POTENTIAL FOR STRONG STORMS OVER
MUCH OF THE AREA THURSDAY AND FRIDAY, SHIFTING PROGRESSIVELY
SOUTHEASTWARD SATURDAY AND SUNDAY. SO, LOOKS LIKE WE ARE STEPPING
INTO A MORE ACTIVE CONVECTIVE PATTERN ONCE WE MOVE PAST RELATIVELY
QUIET DAYS TUESDAY AND WEDNESDAY. CHAMBERS
AVIATION
00Z UPDATE...
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED TO MOVE
WEST TO EAST DURING THE EVENING AND OVERNIGHT HOURS. BRIEF MVFR
CONDITIONS ARE POSSIBLE UNDER ANY THUNDERSTORMS. SOUTHEAST MT HAS
ABOUT A 20% CHANCE FOR FOG/LOW STRATUS AFTER 06Z MONDAY,
PRECEDING OR MIXED WITH LIGHT RAIN. THERE IS ABOUT A 10-20%
CHANCE FOR STRONG TO SEVERE THUNDERSTORMS TO DEVELOP FOR AREAS
EAST OF BILLINGS (KSHR, KMLS) BEGINNING AROUND NOON MONDAY LASTING
THROUGH THE EARLY EVENING. THE MAIN THREAT WITH THESE STORMS WILL
BE LARGE HAIL, STRONG WINDS AND HEAVY RAIN. TS
PRELIMINARY POINT TEMP/POPS
MON TUE WED THU FRI SAT SUN
-----------------------------------------------------------
BIL 056/072 050/075 052/077 053/082 057/088 059/076 052/069
36/T 31/U 01/B 13/T 21/B 47/T 63/T
LVM 047/073 043/075 045/077 048/080 051/082 049/068 041/060
34/T 20/U 01/B 13/T 12/T 58/T 86/T
HDN 054/073 048/075 048/077 051/083 054/089 057/079 050/070
56/T 21/U 01/B 12/T 21/B 46/T 64/T
MLS 052/071 049/072 047/074 051/081 056/085 059/079 053/070
37/T 30/U 00/B 02/T 31/B 55/T 54/T
4BQ 051/072 050/071 047/073 052/080 057/085 061/080 054/072
37/T 70/U 02/W 13/T 51/B 35/T 75/T
BHK 047/071 045/070 043/071 047/077 052/080 056/079 051/070
26/T 60/U 00/B 02/T 31/B 46/T 75/T
SHR 047/072 046/070 044/073 048/080 051/086 054/076 046/069
56/T 71/B 15/T 36/T 31/B 36/T 67/T
BYZ WATCHES/WARNINGS/ADVISORIES
MT...NONE.
WY...NONE.
WEATHER.GOV/BILLINGS
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